class Solution {
    public String toLowerCase(String s) {
        StringBuilder stringBuilder = new StringBuilder();
        for (int i = 0;i < s.length();i ++) {
            char ch = s.charAt(i);
            if (Character.isLetter(ch)) {
                if (!Character.isLowerCase(ch)) {
                    ch = (char) (ch + 32);

                }
            }
            stringBuilder.append(ch);
        }
        return stringBuilder.toString();
    }
}